Selective signal receiving circuit



Nov. 12, 1946.

B. J. HENDERSON I 7 2,411,091 SELECTIVESIGNAL RECEIVING CIRCUIT I Filed May 30, 1944 2 Sheets-Sheet 1 176.

RECE/VER 70 (ALL .TRANSHNWER OU UT BELL sw/rzlm's Nov. 12, 1946.

B. J. HENDERSON SELECTIVE SIGNAL RECEIVING CIRCUIT Filed May 30, 1944 2 Shets-Sheet 2 Patented Nov. 12, 1946 oFFic-E Y SELECTIVE SIGNAL RECEIVING "CIRCUIT Bryan Jam-es Henderson, London, England, assignorof one-half to John GJMurdo'ck &Com- ,pany Limited, London, England, a companyof the "United Kingdom of Great Britain and Northern Ireland Application May 30, 1944, Serial No. 538,003 In Great Britain May 24, 1943 'The object of the .present invention is to enable .aradio line .or other signal receiving station to be called'by number, call-sign, or code, and to signal the fact of the call, in the same manner as with wired automatic telephone systems, even though the receiver is not in operation at the time, at 'the same time indicating to the caller, by means of a return signal that the receiving apparatus is being called.

The apparatus is responsive to trains of impulses at measured intervals for each letter or figure of the code, and to this end employs in known manner the hatching-magnet-operated wiperswitches of automatic telephone exchanges. A further object of the invention, theretore, is to provide against .false operation from interference and other influences to which radio receiving ap-. paratus is subject, and the invention consists in the circuit arrangements employed 'to this end. These are "illustrated in the accompanying drawings, wherein Fig. 1 is a circuit diagram-cf signal recording apparatusaccording to the invention, Fig. 2 is a circuit diagram of a modification of a part of Fig. 1, and Fig. 3a further modification to to be used in conjunction with Figs. 1 and 2. Con- .tacts are shown in the normal, or rest, position.

To make a call trains of impulses corresponding to the code areinitiated at a transmitter by means equivalent to the dialling apparatus of automatic telephones. The output of such transmitter consists of trains of impulses in corre spondence withthose of the call. These are applied to the terminals CA (Fig. 1) whereby the sensitive relay R is operated intermittently in correspondence with the impulses. This relay is preferably adjustable in respect of its sensitivity. The closing of the single contact RI on this relay operates the heavier duty relay L, the contact Ll of which closes a circuit for relay A via conductor 3 to negative main and acircuit in parallel there-' to 'for relay via conductor 4 and contact SI. Contact L2 of relay L operates the magnet of wiper or selector switch SW1 via conductors 5 and 6 when the contact CI of relay 0 has been closed. Relay C is shrouded for slow release, and therefore remains closed throughout the train of impulses. Relay A is also shrouded and remains closed, its contact A closing the delayed-opening relay B, the contact Bl of which prepares a cireuit via conductor 1 for a current supply to the wiper of section 2 of wiper switch SWI. The current supply for this circuit is withheld by the -t'hrowingover of contact Al, and this prevents f operation of intermediate numbers Whilst the switch is wiping; ContactBZ closes a circuit for 3 Claims. (Cl. 177-353) relay S via conductors 8 and 6, the contacts s] and S2 of which change over the circuits to "-rlay C from contact L1 so that thereafterthe trai-nof impulses retains relay 0 closed on the return strokes of contact Ll.

The opening of contact "S'l causes "relay (3 to drop out and thereby open switch magnet-circuit at CI to prevent burningout of the magnet if a continuously received signal causes-relay L to remain closed. Relay C-couldnot, therefore, be held closed at all by the intermittent closing of contacts Ll except for the alternative circuit provided for closureon the return strokes of-contact L'l Winding a of relay F is connectedto that contact on section 2 of wiper switch SWI corresponding to the first letter or figure of the code, and when the corresponding number of impuls'es'has been received, the wiper switch will come to rest on this contact. 'On the cessation of the train of impulses, relay A drops out and its .contactAl completes the circuit through the wiper of section 2 of wiper switch SW1. Asrelay B has delayed opening, contact B1 "in the said circuit remains closed for a suflicient time after contact Al has released relay B to enable a current'impulse through the wiper to operate relay F. Contact Fl 01 relay'F closes the operating circuit of delayed action or time-limit relay THA via conductor 9, contact Z2, conductors l0 and. II, and contact Zl, and contact F2 closes a circuit "for holding winding b of relayF, this circuit passing via conductors l2 and I3 and contacts W|,THAI and Z1 Opening of relay B after a current impulse has been sent through contact Bl causes the latter contact to connect the supply of current to the wiper of section I of the switch SWI. This section is provided with a continuous semi-circular contact engaged by the wiper in all positions except the rest position. Alternatively, a section of separate contacts all connected may be used, provided the wiper is arranged so that it must always touch at least two at a time. In the rest position no circuit is completed by contact Bl when in the on position of itsrelay but once the switch has operated to any number, another circuit will be completed for the magnet through the make and break contacts mb which are operated by the magnet. The latter then notches the switch round continuously until the wiper reaches the starting point, when the circuit opens. The :set-

' ting of the transmitter is arranged to give time for this return operation before a second train of impulses can be commenced. When relays A,

. once.

B and S drop out, the original circuits for C are restored, so that C also drops out by the opening of the circuit at S2. Otherwise relay C would remain closed when contact LI remains in the off position, All parts are now in the original position except relay F and the circuits controlled by it, which remain closed.

The foregoing operations are repeated during the next train of impulses corresponding to the next figure of the code, and when Wiper switch SWI comes to rest, winding a of relay G is energised, and the contact G2 closes a circuit for its holding winding b. In the same manner, as many relays FK may be operated as there are figures in the code, and closure of the last contact K2 operates relay X by its operating winding b, the circuit being through contacts F2-K2 in series, conductor I3, and contacts WI, THAI and ZI. The contact XI of this relay is arranged to give the call signal to anyone present at the station, the circuit for this being continued from terminals CB, and the contact X2, in a circuit continued from terminals CC, likewise sets in operation a transmitter to send back a signal indicating that the call is being made (known as the fringing tone in automatic telephone systems). Contact X3 closes a circuit for the holding'winding a of the relay to maintain the call signal and ringing tone when delayed action relay THA operates. As there is no provision for discontinuing an unanswered call at the instigation of the caller, .the circuit of winding a of relay X contains a thermal or other time lag relay TX which will open the circuit at its contact TXI after a signal has been given for a reasonable length of time.

It shouldbe observed that the initial stages of the operations will be performed by calls to any other station commencing with the same figure or figures, but that the signal'of a call to the present station can only be given when the last figure of the code has been transmitted after all the others have been given in their correct order. However, where a call to another station with a code commencing with the same figures has been picked up by the present station, it remains an uncompleted call, and the operation of the time-lag relay TI-IA after a predetermined interval opens the holding circuit of relay F and of any of the others as far as J which may have operated. The time-lag relay also operates to disconnect and restore the apparatus if for any reason a, call to the present station is not completed within the said time, otherwise the call is bound to be completed falsely sooner or later whenever a figure the same as the next in the code is sent out during a call to any other station. Owing to the time a delayed action relay may take to reset after operation, as for example, where a thermal relay has to cool it may not be possible to use it again immediately, and this may mean an inconvenient delay before the station can be called, especially in the interruption of a call, as where a caller (maybe through accident) takes too long to complete the code or commences at the tail end of a functioning of the time-lag relay due to some interference, and gets out off at To meet this case, provision is .made for an alternative time-lag or time-limit relay THB to be brought into use immediately if required. If required means if a call has to be made or continued. Hence, the partly expired timelag relay is caused to reset or the alternative relay is to be brought into use by the caller, otherwise an unnecessary continualchange-over of timelag relays would oocurwith every false and unwanted impulse received. Since a caller, however, cannot know the state of thetime-lag relays, he can either take his chance that he calls when a relay is open, or will open before the call is completed, in either case getting no ringing tone and having to commenceagain, or he can send the time-lag relay change-over or resetting signal in the first place in any event, and so be sure of getting on to a normal relay at once, even though the one from which he changes over is also normal. A single connection sufiices to change over or reset the time-lag relays and this can be given by a-special signal sending a different number of impulses from any other code figure, as for example when dialling 0.

When the time-lag relays are changed over, the wiper switch section 2 sends its first impulse along the line I4 and the relay Z is operated, the circuit being via contacts W3 and VI and conductor I5. Contacts ZI and Z2 then change over the time-lag relay operating circuits whilst contact Z3 closes a circuit for relay Y via conductor I6 and contacts THBI and ZI. Contact YI then closes and holds relay Z, contact Y2 prepares a circuit for relay W, contact C2 being open during the train of signal impulses, and contact Y3 closes the operating circuit of relay TI-lIB. It is necessary thus to start operating the relay, otherwise the relays appertaining to this operation would remain locked if no code call were commenced after giving the change-over signal and nothing further could be done. When contact C2 falls back just after the operating impulses for relay Z has been given, relay W is operated by current via conductor I1 and contact Y2 and its contact W2 completes its holding circuit so that relay W remains closed during the opening of C2 by the further signal impulses of the code. Contact WI of this relay changes over the holding circuit of relays F-K (via conductor I3) from time relay 'IHA to time relay THB, via conductor IS an instant (the drop-out delay of relay C) after contacts ZI and Z2 have closed 7 If contacts WI and ZI closed simultaneously with both time-lag relays closed, any of relays F-J which happened to have been ust operated by an interference would remain closed and a correct start of the codesignalsJcould'not be made. The special signal to changeover the time-lag relays therefore also serves the purpose of correctly setting the apparatus to receivea call should one happen to be commenced while contacts FI and F2 are closed'due to an interference. Contact W3 prepares a circuit for relay V to be completed by the next given change-over or resetting signal through conductor I4. When the next change-over or resetting signal is given, relay V closes and its contact VI releases relay Z causing contact ZI and Z2 to change back the circuit to time-lag relay THA. 'Relay W has slow release, therefore holds contact WI for conductor l3, when'opening of contact Z3 releases relay Y, (and its contact Y2 in circuit of relay W), until after contacts ZI and Z2 have operated, for the reason already explained. Contact ,W3 then prepares the circuit for operating relay Z by the next change-over signal.

Fig. 2 shows an arrangement forialtering the the leads from the contacts of each section can be connected as required to any of the code num ber contacts of section 2 of switch SWI. This can be done by connecting in a fixed predetermined manner each contact in each section of switch SW2 to any one of a plurality of bus bars 22 each of which is connected to a contact of section 2 of switch SWI, or switching means may be interposed to vary these connections.

To alter the code, the magnet of wiper switch SW2 is notched by a hand key 71. to step the switch to a diiferent code number, or the switch may be rotated manually if accessible. The codes must always be passed through in the same order, although any one can be obtained by stepping the switch right around to the starting position. The circuits for the relays F-K will then only be completed when the code for which the switch SW2 is set is signalled.

If desired, the code may be changed automatically on the completion of any call, but in this case only the next following code number on the setting can be obtained. This is shown in Fig. 3. The relays GK are provided with additional contacts GI-KI all in series, and in series with contact Fl of relay F. When all these contacts have been closed on the completion of the code signals, the magnet of switch SW2 is energized and the switch notched to the position of another code setting.

I claim:

1. In a signal system, a signal receiving station including a plurality of code relays, means responsive to impulses representing an incomplete or a complete code signal for energizing one or more of said relays, a first and a second time-limit relay each having contacts connected to de-energize said code relays after a predetermined time in the event said code relays are energized by an incomplete code signal, means for energizing the first of said time-limit relays, and means operable by a second code signal for en- 6 ergizing the second and de-energizing the first of said time-limit relays should the time-limit of said first relay be partially exhausted.

2. In a signal system, a signal receiving station including a plurality of code relays, means responsive to impulses representing an incomplete or a. complete code signal for energizing one or more of said relays, a first and a second timelimit relay each having contacts connected to deenergize said code relays upon the operation of said time-limit relays in the event said code relays are energized by an incomplete code signal, means for energizing the first of said time-limit relays, means operable by a second code signal for energizing the second and de-energizing the first of said time-limit relays should the timelimit of said first relay be partially exhausted, and means responsive to the operation of said second time-limit relay for de-energizing the second and energizing the first of said time-limit relays.

3. In a signal system, a signal receiving station including a plurality of code relays, a selector switch having a stepping magnet and a plurality of code number contacts, and means responsive to impulses representing a code signal for energizing said stepping magnet, a second selector switch having a stepping magnet and a plurality of sections and cooperating switch arms, the number of sections corresponding to the number of said code relays, each contact'of each of said sections being connected to each of said code number contacts of the first selector switch, said switch arms being connected respectively to en ergize said code relays, said code relays being energized in a predetermined sequence, and a contact closed by the operation of the last code relay to be energized, said contact being connected to energize the stepping magnet of said second selector switch, whereby to change the code of said station on the completion of each call.

BRYAN JAMES HENDERSON. 

